In recent years, magnetic disk devices based on Two-Dimensional Magnetic Recording (TDMR) and comprising a plurality of read heads have been developed. In TDMR, a read/write (R/W) offset may occur between a write head and the plurality of read heads. Thus, in a TDMR magnetic disk device, if data is read which is written to a position separated, by an R/W offset, from a position with the read head positioned thereat, the position of a reference read head which is to read data is corrected based on the R/W offset between the write head and the reference read head. To correct the position of the reference read head in this manner, the TDMR magnetic disk device measures, at a prescribed track of the disk, the R/W offset between the write head and each of the plurality of read heads, and holds the measured R/W offsets in a nonvolatile memory or the like. Furthermore, an increased track density (Track Per Inch: TPI) has led to the need to measure the R/W offset at more tracks and hold the measured R/W offsets in order to improve measurement accuracy of an R/W offset correction value. Therefore, this may increase the time taken to measure the R/W offset correction value for each head and a data capacity for holding the measured R/W offsets.